1. Field of the Invention
The present invention relates to the technical field of image processing and, more particularly, to a method and device of skin tone optimization in a color gamut mapping system.
2. Description of Related Art
FIG. 1 is a schematic diagram of a typical color enhancement system 100. The color enhancement system 100 is comprised of an RGB to HSV color space transform unit 110, a color enhancement unit 120, and an HSV to RGB color space transform unit 130. The RGB to HSV color space transform unit 110 transforms pixels of an input image signal from an RGB color domain to an HSV color domain. The color enhancement unit 120 enhances the color saturation based on a gain signal S_gain(H) and adjusts the hue based on a color shift signal H_shift(H). The HSV to RGB color space transform unit 130 transforms a signal output by the color enhancement unit 120 from the HSV color domain to the RGB color domain. However, the typical color enhancement system 100 is subjected to an over-enhanced skin tone while the color saturation is enhanced according to the signal S_gain(H), so that the skin tone becomes brown and unnatural after the image processing.
In U.S. Pat. No. 8,265,389 granted to Hung, et al. for a “Color enhancement for digital images”, it first enhances the saturation of the YCbCr color domain and detects the shades of different colors, and then uses an exposure index (EI) and color temperature D to thereby correct the enhancement factors for different enhancements. However, such a way cannot separate the skin tones for applying different processes.
In U.S. Pat. No. 6,904,165 granted to Lu for a “Color image processing apparatus and method for color enhancement”, it enhances the color saturation without transforming the RGB color domain to the HSV/HSB color domain, but it does not perform any processing for the skin tones.
In U.S. Pat. No. 7,986,833 granted to Shen, et al. for an “Image processing method and apparatus for color enhancement and correction”, it avoids generating the clipping effect caused by over-enhancing the color saturation, but it also does not perform any processing for the skin tones and thus the problem of brown and unnatural skin is still encountered.
Therefore, it is desirable to provide an improved color enhancement method and device to mitigate and/or obviate the aforementioned problems.